Unilateral condylar hyperplasia: a 3-dimensional quantification of asymmetry

A Review of Three-Dimensional Facial Asymmetry Analysis Methods

Three-dimensional symmetry and coordination are important factors in facial aesthetics, and analysis of facial asymmetry is the basis for clinical diagnosis, treatment, and doctor–patient communication. With the development of three-dimensional measurement and data analysis technology, facial asymmetry analysis methods are mainly based on facial anatomic landmarks, original-mirror alignment algorithm, facial anthropometric mask, and artificial intelligence. This review summarizes the methods of three-dimensional facial asymmetry analysis, and current research progress in the field. The advantages and limitations of various methods are analyzed and discussed to provide a reference for oral clinical application.

A mathematical algorithm of the facial symmetry plane: Application to mandibular deformity 3D facial data

The three-dimensional (3D) symmetry reference plane (SRP) is the premise and basis of 3D facial symmetry analysis. Currently, most methods for extracting the SRP are based on anatomical landmarks measured manually using a digital 3D facial model. However, as different clinicians have varying definitions of landmarks, establishing common methods suitable for different types of facial asymmetry remains challenging. The present study aimed to investigate and evaluate a novel mathematical algorithm based on power function weighted Procrustes analysis (PWPA) to determine 3D facial SRPs for patients with mandibular deviation. From 30 patients with mandibular deviation, 3D facial SRPs were determined using both our PWPA algorithms (two functions) and the traditional PA algorithm (experimental groups). A reference plane, defined by experts, was considered the 'truth plane'. The 'position error' index of mirrored landmarks was created to quantitatively evaluate the difference among the PWPA SRPs and the truth plane, including overall differences and regional differences of the face (upper, middle and lower). The 'angle error' values between the SRPs and the truth plane in the experimental groups were also evaluated in this study. Statistics and measurement analyses were used to comprehensively evaluate the clinical suitability of the PWPA algorithms to construct the SRP. The average angle error values between the PWPA SRPs of the two functions and the truth plane were 1.21 ± 0.65° and 1.18 ± 0.62°, which were smaller than those between the PA SRP and the truth plane. The position error values of mirrored landmarks constructed using the PWPA algorithms for the whole face and for each facial partition were lower than those constructed using the PA algorithm. In conclusion, for patients with mandibular deviation, this novel mathematical algorithm provided a more suitable SRP for their 3D facial model, which achieved a result approaching the true effect of experts.

[Preliminary clinical application verification of complete digital workflow of design lips symmetry reference plane based on posed smile]

OBJECTIVE

To automatically construct lips symmetry reference plane (SRP) based on posed smile, and to evaluate its advantages over conventional digital aesthetic design.

METHODS

Eighteen subjects' three-dimensional facial and dentition data were gathered in this study. The lips SRP of experimental groups were used with the standard weighted Procrustes analysis (WPA) algorithm and iterative closest point (ICP), respectively. A reference plane defined by experts based on regional ICP algorithm, served as the truth plane. The angle error values between the lips SRP of WPA algorithm in the experimental groups and the truth plane were evaluated in this study, and the lips SRP of ICP algorithm of the experimental groups was calculated in the same way. The lips SRP based on posed smile as a reference for aesthetic design and evaluate preliminary clinical application.

RESULTS

The average angle error between the lips SRP of WPA algorithm and the truth plane was 1.78°±1.24°, which was smaller than that between the lips SRP of ICP and the truth plane 7.41°±4.31°. There were significant differences in the angle errors among the groups (P < 0.05). In the aesthetic design of anterior teeth, automatically constructing the lips SRP of WPA algorithm based on posed smile and the original symmetry plane by re-ference compared with the prosthetic design, the subjects' scores on the lips SRP of WPA algorithm based on posed smile (8.48±0.57) were higher than those on the original symmetry plane (5.20±1.31).

CONCLUSION

Automatically constructing the lips SRP of WPA algorithm based on posed smile was more accurate than ICP algorithm, which was consistent with the truth plane. Moreover, it can provide an important reference for oral aesthetic diagnosis and aesthetic analysis of the restoration effect. In the aesthetic design of anterior teeth, automatically constructing the lips SRP of WPA algorithm based on posed smile can improve the patients' satisfaction in esthetic rehabilitation.

Valid 3D surface superimposition references to assess facial changes during growth

Currently, the primary techniques applied for the assessment of facial changes over time utilize 2D images. However, this approach has important limitations related to the dimensional reduction and the accuracy of the used data. 3D facial photography has been recently introduced as a risk-free alternative that overcomes these limitations. However, the proper reference areas that should be used to superimpose serial 3D facial images of growing individuals are not yet known. Here, we tested various 3D facial photo superimposition reference areas and compared their outcomes to those of a standard anterior cranial base superimposition technique. We found that a small rectangular area on the forehead plus an area including the middle part of the nose and the lower wall of the orbital foramen provided comparable results to the standard technique and showed adequate reproducibility. Other reference areas that have been used so far in the literature were less reliable. Within the limitations of the study, a valid superimposition reference area for serial 3D facial images of growing individuals is suggested. The method has potential to greatly expand the possibilities of this highly informative, risk free, and easily obtained 3D tool for the assessment of facial changes in growing individuals.

[A method for constructing three-dimensional face symmetry reference plane based on weighted shape analysis algorithm]

OBJECTIVE

To establish a novel method based on three-dimensional (3D) shape analysis and weighted Procrustes analysis (WPA) algorithm to construct a 3D facial symmetry reference plane (SRP), automatically assigning weight to facial anatomical landmarks. The WPA algorithm suitability for commonly observed clinical cases of mandibular deviation were analysed and evaluated.

METHODS

Thirty patients with mandibular deviation were recruited for this study. The 3D facial SRPs were extracted independently based on original-mirror alignment method. Thirty-two anatomical landmarks were selected from the overall region by three times to obtain the mean coordinate. The SRP of experimental groups 1 and 2 were using the standard Procrustes analysis (PA) algorithm and WPA algorithm, respectively. A reference plane defined by experts based on regional iterative closest point (ICP) algorithm, served as the ground truth. Three experts manually selecting facial regions with good symmetry for original model, and common region was included in the study. The angle error values between the SRP of WPA algorithm in the experimental group 1 and the truth plane were evaluated in this study, and the SRP of PA algorithm of experimental group 2 was calculated in the same way. Statistics and measurement analysis were used to comprehensively evaluate the clinical suitability of the WPA algorithm to calculate the SRP. A paired t-test analysis (two-tailed) was conducted to compare the angles.

RESULTS

The average angle error between the SRP of WPA algorithm and the ground truth was 1.53°±0.84°, which was smaller than that between the SRP of PA and the ground truth (2.06°±0.86°). There were significant differences in the angle errors among the groups (P < 0.05). For the patients with severe mandibular deviation that the distance between pogonion and facial midline greater than 12 mm, the average angle error of the WPA algorithm was 0.86° smaller than that of the PA algorithm.

CONCLUSION

The WPA algorithm, based on weighted shape analysis, can provide a more adaptable SRP than the standard PA algorithm when applied to mandibular deviation patients and preliminarily simulate the diagnosis strategies of clinical experts.

A novel method for 3D face symmetry reference plane based on weighted Procrustes analysis algorithm

BACKGROUND

We aimed to establish a novel method, using the weighted Procrustes analysis (WPA) algorithm, which assigns weight to facial anatomical landmarks, to construct a three-dimensional facial symmetry reference plane (SRP) for mandibular deviation patients.

METHODS

Three-dimensional facial SRPs were independently extracted from 15 mandibular deviation patients using both our WPA algorithm and the standard PA algorithm. A reference plane was defined to serve as the ground truth. To determine whether the WPA SRP or the PA SRP was closer to the ground truth, we measured the position error of mirrored landmarks, the facial asymmetry index (FAI) error, and the angle error for the global face and each facial third partition.

RESULTS

The average angle error between the WPA SRP and the ground truth was 1.66 ± 0.81°, which was smaller than that between the PA SRP and the ground truth. The position error of the mirrored landmarks constructed using the WPA algorithm in the global face (3.64 ± 1.53 mm) and each facial partition was lower than that constructed using the PA algorithm. The average FAI error of the WPA SRP was - 7.77 ± 17.02 mm, which was smaller than that of the PA SRP.

CONCLUSIONS

This novel automatic algorithm, based on weighted anatomic landmarks, can provide a more adaptable SRP than the standard PA algorithm when applied to severe mandibular deviation patients and can better simulate the diagnosis strategies of clinical experts.

Differences in dental arch characteristics between genders in patients with suspected condylar hyperplasia in a North Sumatra subpopulation: a cross-sectional study

Background: Condylar Hyperplasia (CH) is a self-limiting mandibular condyle disorder that shows asymmetry progress in conjunction with associated occlusal changes as long as condylar growth is still active and leads to facial asymmetry. This study aimed to analysis the difference of dental arch characteristics  based on genders in orthodontic patients with suspected CH in a North Sumatra subpopulation.

Methods: This is a retrospective study of suspected CH patient’s clinical records who sought for the initial orthodontic treatment between January 2015 to March 2019. Patient with facial asymmetry (based on photography, posterior crossbite and midline deviation), the positive temporomandibular joint disorder in functional analysis, and no history of facial trauma were included in the study. Dental arch asymmetry was based on the measurement of dental midline deviation, canine tip in the dental arch, the distance of the upper canines from the palatal suture, and inter canine distance. The evaluation of dental arch was achieved by comparing arch width and length.

Results: There was a significant difference (p<0.05) of upper canine distance from the palatal suture in female patients when evaluating upper dental arch asymmetry. There was a moderate correlation (r=0.379) in midline deviation between upper and lower dental arch. The dimension and dental arch form were mid and flat, and there was moderate correlation (r=0.448) between the upper and lower dental arch form in these suspected CH patients.

Conclusion: Indeed skeletal asymmetry, the evaluation of the dental arch characteristic symmetry and arch form showed asymmetric occlusal characteristics in orthodontics patient with suspected  CH in the North Sumatera subpopulation. In treating these patients, we recommend the plaster cast evaluation as essential and routine procedure in order to understand the complexity of occlusal change due to active growth of condylar and limitation in radiography evaluation.

Assessment of relative uptake by mandibular condyles in a "normal" population

Hyperplasia of the mandibular condyle is self-limiting, but can lead to facial asymmetry, malocclusion, pain, and dysfunction of the temporomandibular joint (TMJ). Bone scintigraphy, particularly with single photon emission computed tomography (SPECT), is effective in assessing relative condylar uptake, but we know of no standardised methods or values. Our aim, therefore was to validate the values currently used to measure relative condylar uptake in our population. Between December 2015 and June 2018 44 patients had skull SPECT (15 male and 29 female patients, whose ages ranged from 4-33 years). They were having bone scans (hydroxydiphosphonate (HDP) -^99MTc, 740 MBq ev) for unrelated reasons and had no known abnormalities of the head, facial asymmetry, or symptoms of the TMJ. Two research workers measured the relative uptake between the condyles using the summed transaxial images. The Hospital Ethics Committee approved the investigation. The maximum difference in condylar uptake was 8.33% with research worker 1 and 8.77% with research worker 2, and the mean (SD) differences were 3.03 (0.17) % and 3.29 (0.18) %, respectively. Data were tested for normality, and the t test and one-way ANOVA were used to assess the significance of differences. None was found in total counts either between sexes or age groups, and there were none between the total counts measured by the two research workers. We conclude that our results are within the published ranges, and the variation in condylar uptake was less than 5% in 37/44 patients, and in none was it 9% or more. When the results indicate less than 10%, but there is a high clinical suspicion of active hyperplasia, surgeons should use their clinical judgement to decide whether condylar surgery is required.

MiR-15b is a key regulator of proliferation and apoptosis of chondrocytes from patients with condylar hyperplasia by targeting IGF1, IGF1R and BCL2

OBJECTIVE

This study aimed to explore potential microRNAs (miRNAs), which participate in the pathological process of condylar hyperplasia (CH) through targeting specific proliferation- and apoptosis- related genes of chondrocytes.

METHODS

Insulin-like growth factor 1 (IGF1), IGF1 receptor (IGF1R) and B-cell CLL/lymphoma 2 (BCL2) in CH cartilage were detected by real-time polymerase chain reaction (PCR), Western blot, immunohistochemistry and immunofluorescence. MiRanda and TargetScanS algorithms were used to predict certain miRNAs in CH chondrocytes concurrently modulating the above three genes. MiR-15b was screened and identified using real-time PCR. After transfection of miR-15b mimics or inhibitor into CH chondrocytes, expression of the above three genes was detected by real-time PCR and western blot, meanwhile, cell proliferation and apoptosis was examined by CCK8, cell cycle assays, flow cytometry and Hoechst staining. Dual luciferase activity was performed to identify the direct regulation of miR-15b on IGF1, IGF1R and BCL2.

RESULTS

Expression of IGF1, IGF1R and BCL2 increased in CH cartilage. Seven microRNAs concurrently correlated with IGF1, IGF1R and BCL2. Among them, only miR-15b significantly changed in CH chondrocytes. Overexpression of miR-15b in CH chondrocytes suppressed the expression of IGF1, IGF1R and BCL2, while it increased when miR-15b was knockdown. Furthermore, miR-15b suppressed their expression by directly binding to its 3'-UTR in these cells. Besides, miR-15b hampered chondrocytes proliferation through targeting IGF1 and IGF1R and accelerated chondrocytes apoptosis through targeting BCL2.

CONCLUSION

Suppressed miR-15b contributed to enhanced proliferation capacity and weakened apoptosis of chondrocytes through augmentation of IGF1, IGF1R and BCL2, thereby resulting in development of CH.

Measuring asymmetry from high-density 3D surface scans: An application to human faces

Perfect bilateral symmetry is the optimal outcome of the development of bilateral traits in the absence of developmental perturbations. Any random perturbation in this perfect symmetrical state is called Fluctuating Asymmetry (FA). Many studies have been conducted on FA as an indicator of Developmental Instability (DI) and its possible link with stress and individual quality in general and with attractiveness, health and level of masculinity or femininity in humans. Most human studies of facial asymmetry use 2D pictures and a limited number of landmarks. We developed a protocol to utilize high-density 3D scans of human faces to measure the level of asymmetry. A completely symmetric spatially dense anthropometric mask with paired vertices is non-rigidly mapped on target faces using an Iterative Closest Point (ICP) registration algorithm. A set of 19 manually indicated landmarks were used to validate the mapping precision. The protocol's accuracy in FA calculation is assessed, and results show that a spatially dense approach is more accurate. In addition, it generates an integrated asymmetry estimate across the entire face. Finally, the automatic nature of the protocol provides a great advantage by omitting the tedious step of manual landmark indication on the biological structure of interest.

Comparison of temporomandibular joint shape and size in patients with facial asymmetry

OBJECTIVE

To examine the morphologic similarities and differences in mandibular condyle and glenoid fossa between the deviated and non-deviated sides in patients with facial asymmetry using statistical analysis.

METHODS

One hundred eighty-four patients (95 men, 89 women; mean age, 22.30 ± 3.87 years) with facial asymmetry were examined with cone-beam computed tomography (CBCT). Shape analysis was performed to compare the shapes and sizes of the condyle and fossa between the deviated and non-deviated sides in the frontal and lateral aspects. Ordinary Procrustes analysis (OPA) was used to determine shape variations of the fossa and condyle.

RESULTS

Shape variations derived from ordinary sum of squares (OSS) suggested that, in the frontal aspect, there was a difference between the two sides in both the fossa and condyle (P < 0.05). In the lateral aspect, there was no difference in fossa shape between the two sides (P > 0.05); however, the shape of condyle was different between the non-deviated and deviated sides (P < 0.05). Size comparison in OPA matching and centroid size (CS) in the frontal aspect demonstrated that the non-deviated side was larger than the deviated side. In the lateral aspect, fossa showed no difference in CS between the two sides (P > 0.05); however, the non-deviated side was larger than the deviated side for condyle (P < 0.05).

CONCLUSIONS

Morphometric differences in condyle and fossa between the deviated and non-deviated sides were observed. Structures of the non-deviated side were relatively larger than those of the deviated side, except for fossa in the lateral aspect.

Mandibular asymmetry: a three-dimensional quantification of bilateral condyles

INTRODUCTION

The shape and volume of the condyle is considered to play an important role in the pathogenesis of the mandibular deviation. Curvature analysis is informative for objectively assess whether the shape of the condyles matches that of the glenoid fossa. In this study, a three-dimensional (3-D) quantification of bilateral asymmetrical condyles was firstly conducted to identify the specific role of 3-D condylar configuration for mandibular asymmetry.

METHODS

55 adult patients, 26 males (26 ± 5 yrs) and 29 females (26 ± 5 yrs), diagnosed with mandibular asymmetry were included. The examination of deviation of chin point, deviation of dental midlines, inclination of occlusal plane, and depth of the mandibular occlusal plane were conducted. After the clinical investigation, computed tomography images from the patients were used to reconstruct the 3-D mandibular models. Then the condylar volume, surface size, surface curvature and bone mineral density were evaluated independently for each patient on non-deviated and deviated sides of temporomandibular joint.

RESULTS

Both the condylar surface size and volume were significantly larger on deviated side (surface size: 1666.14 ± 318.3 mm2, volume: 1981.5 ± 418.3 mm3). The anterior slope of the condyle was flatter (0.12 ± 0.06) and the posterior slope (0.39 ± 0.08) was prominently convex on the deviated side. The corresponding bone mineral density values were 523.01 ±118.1 HU and 549.07 ±120. 6 HU on anterior and posterior slopes.

CONCLUSIONS

The incongruence presented on the deviated side resulted in a reduction in contact areas and, thus, an increase in contact stresses and changes of bone density. All aforementioned results suggest that the difference existing between deviated and non-deviated condyles correlates with facial asymmetrical development. In mandibular asymmetry patients, the 3-D morphology of condyle on deviated side differ from the non-deviated side, which indicates the association between asymmetrical jaw function and joint remodeling.